The present invention relates generally to surveillance devices. More particularly, the invention relates to an apparatus and a method for passive or active acoustic surveillance.
There are many situations in which surveillance devices, or other devices that are capable of providing information about the location and movement of people, are valuable tools. One exemplary situation occurs when rescuers are attempting to locate disaster victims. Other examples include criminal or terrorist situations where hostages have been taken or where police must enter a building in which an armed or dangerous suspect may be hiding. These types of situations present dangerous scenarios for both the hostages and the police or other law-enforcement agents who are responsible for handling the situation. The danger arises, in large part, because the law enforcement agents typically cannot detect with certainty the number and location of individuals within the building. In addition, the law enforcement agents often cannot detect a precise location of particular individuals, such as suspects, within the building thus complicating the agents' ability to resolve the situation.
Therefore, surveillance devices capable of providing detailed information about the number, location, and movement of the individuals within the building can aid the law enforcement agents in making tactical decisions in these types of situations. If the agents are able to monitor the location and movement of those inside the building, the agents make better decisions on how to resolve the situation quickly and safely.
Most surveillance devices operate on a line of sight principle, requiring visual detection of individuals. However, if a clear view into the building is not available, the law enforcement agents must resort to other types of surveillance methods to gather information about the number, location, and movements of the individuals within the building. A surveillance device using radar signals to locate and track people within the building is one possibility. However, radar signals do not travel well through metal. Thus, if the building contains metal structures, as often occurs, the information provided by the radar surveillance may not be capable of detecting individuals in the building with a reasonable degree of accuracy.
In light of the foregoing there is a need for a method and device for providing surveillance information about sources of acoustic energy positioned behind a structure.